This invention relates to programmable electronic thermostats, and particularly to such thermostats which control operation of multistage heating apparatus.
A typical multistage heating apparatus comprises a heat pump which provides a first stage of heating, and electrical resistance heaters, sometimes referred to as auxiliary heaters, which provide additional stages of heating. Operation of the auxiliary heaters is less energy efficient than operation of the heat pump so that, for economy, it is desirable that use of the auxiliary heaters be minimized. For example, when the thermostat provides a temperature setback function, it is desirable, for economy, that use of the auxiliary heaters be minimized during the time, sometimes referred to as recovery time, that the heating apparatus is attempting to return the temperature of the controlled space from a setback temperature to a normal comfort temperature.